Exhaust gas filters are being used increasingly to remove harmful substances contained in the exhaust gases of combustion engines. Prior art soot filters, produced from ceramic materials and employed in conjunction with diesel engines, feature filter bodies whose inlet channels admit hot engine exhaust gases that penetrate the porous filter walls bordering such channels and then exit clean through outlet channels. The high operating temperature of conventional exhaust gas filters causes the soot, i.e., carbon trapped in the filter walls, to be converted to gas and ash, which are then expelled together with the exhaust gases out of the exhaust pipe.
The disadvantage of this type of filter is that removal of the carbon soot is determined and also limited by the distribution and the round shape of the pores in the filter wall. A further disadvantage of ceramic filters is that they have a low resistance to sudden temperature changes, local overheating, bumps and knocks.
Also known in the art are exhaust gas catalyzers that are, by means of catalytic processes, able to remove from exhaust gases other harmful components such as carbon monoxide, hydrocarbons and nitrogen oxides. Such catalyzers make use of, for example, filters coated with platinum, rhodium, vanadium or other materials possessing catalytic properties. Besides being very expensive, such filters are limited in both durability and effectiveness.
It has been suggested that the filter body could be manufactured from moulded high-temperature resistant, sintered material. In addition to being able to withstand thermal shock, knocks and bumps, such a filter exhibits high thermal conductivity over a large internal surface area, a physical relationship that is thermally effective especially when the system is employed as a soot filter in diesel engines. This filter, when used for this purpose, facilitates gasification of the soot particles by improving distribution of particulate over the filter fibers and by permitting, by means of a large surface area, optimal effectiveness of the catalytic process.